Medicare beneficiaries underwent 1.2 million cataract surgeries in 1992. Virtually all cataract surgery is performed on an outpatient basis using intravenous sedation and local anesthesia. Past research has documented marked variation in the extent of preoperative, medical laboratory tests performed, physicians' reasons for ordering them, and much uncertainty about their clinical utility and ,cost-effectiveness. Nonetheless, medical laboratory testing (e.g., blood count, electrolytes, chest X-ray, electrocardiogram etc.) prior to cataract surgery is routinely performed, accounting for annual costs of approximately $150 million. We propose to randomize a large cohort of cataract surgical patients to receive or not receive a routine battery of preoperative laboratory tests and 1) compare the rates of intra-, peri-, and short-term postoperative adverse events for the two groups; 2) assess the cost-effectiveness of a routine battery of preoperative medical tests in all cataract surgery patients and in various subsets of patients based on medical history; and 3) develop a practice guideline on the appropriate use of medical tests prior to cataract surgery that is endorsed by the principal relevant medical societies. Twenty thousand patients aged 50 and older scheduled for elective ambulatory cataract surgery will be randomized. All patients will undergo a standardized medical history questionnaire as well as the routine preoperative history and physical performed at each site. Patients meeting specified criteria representing active/symptomatic medical conditions will receive directed medical testing. Adverse medical outcomes occurring intra- and perioperatively up to one week following surgery will be assessed. Our principal hypothesis is that routine preoperative medical laboratory testing for cataract surgery is not cost-effective and may provide no health benefit. Study results also will be relevant to patients undergoing other ophthalmic procedures (e.g., glaucoma and retinal surgery) and to other outpatient elective procedures where the surgery is performed without general anesthesia and blood loss is minimal. Study results will be reviewed by professional medical societies representing ophthalmology, anesthesiology, and internal medicine at a consensus conference at which a practice guideline endorsed by them will be developed, thereby facilitating the reduction of unnecessary testing and the potential savings of considerable health care expenditures.